I had a bad lightning storm over the weekend which caused a capacitor in my amplifier to explode, followed by my right speaker. Total damages are in the 2-3 grand range, so I'm not really happy. Anyway, I happened to have equivalent replacement caps for the amp, and in looking over the board, found that the only part that appeared to be damaged was the one cap, so I replaced them both. I repowered the amp up and found that the left amp is measuring and appearing fine, but the right amp, for which the speaker was also damaged, is making a low level hum noise. I can't figure out what is causing this. None of the parts look damaged, but obviously one of them is.

I have begun testing some of the parts, the main transistors seem to test within spec, and those resistors and diodes I could test also seemed to test ok. From here the only thing I know to do would be to remove parts one by one and test them until I find one out of spec. If I'm going to do that, I might as well just replace them all, which seems silly. Any idea's what the most likely culprit of such a noise would be. Again, I have a single power supply for both channels, and one amp is ok, the other is not. The hum isn't so loud as to over power music, it doesn't change with input volume, but its a loud enough hum to not be normal, plus the other side doesn't do it. Measuring the hum with my frequency setting on my DMM gets it at 120hz. Measuring on my Oscilliscope shows a more complex set of 120hz and its fundamentals, including 60hz. I normally would think power supply, but for only one channel to have this seems strange. I did have to completely take apart the amp and put it back together, any chance I messed up the grounding some how and that is causing it? It's star grounded and I hooked it back up the way it was, which is the same as I would ahve done it if I was doing it myself.

I would guess another capasitor is AWOL, maybe / probably a bypass cap that is now allowing supply line ripple into the circuit and defeating its PSRR. Without a circuit its only a guess - maybe a zener bypass / bias bypass etc etc.

(edit)
Its also possible you did something when re-assembling, even the route a wire takes is important ...

If the amp it more than 10 years old the it might be an idea to replace all the non-psu electros and any lowish voltage film caps if you suspect the amp has seen a big surge ...

it might be worth replacing / adding a transient suppressor

BTW, was it a PSU cap that went ?
What was the damage to the speaker ?

I won't comment on the possible failures leading to your problem, but I will say from experience that Klipsch does a decent job of supporting the Acurus products. I purchased a used ACT-3 preamp a little while back. When I had questions, they answered the next day. When I asked about purchasing a service manual, the tech said that one was never created, but he was kind enough to attach the schematic for the preamp. Apparently, since Klipsch isn't producing the Acurus products anymore, they are pretty nice about free support. It's worth a try.

Yes it was a PSU cap that went, and the speaker was fried, as in the coils melted, as in the woofers no longer move. There was a transient suppressor in the amplifier already, and it was plugged into a surge suppressor. The surge suppressor is fried, and the internal transient suppressors needed replacement in the amp before I got everything like new.

Oddly, after spending 48 hours stewing, the amplifier has quieted down. It is still making a slight hum, which is always made, but this does seem slightly louder than before. There is however a sort of continuous clicking at the output, also down in level, which I don't recall it ever doing. I'm going to take some measurements when my oscilloscope probes come to see how the right channel compares with the left, maybe that will answer more.

I'm not sure if this answers any other questions, but when I examined the capacitors I noticed that only one went, and the one that went had an indentation for the vent, but no vent. Any chance that it was mis-manufactured without the vent plug, making it unable to vent excess pressure? All the other Hitachi capacitors I own myself have red plugs, and the one had a red plug, but the other had a black plug, which looked very different. I tried to look inside and see if this plug could have just been a different color vent plug, but it doesn't look the same as the red plug in the other cap. Not sure if that had anything to do with it.